1. Field of the Invention
This invention relates to a digital data recording apparatus, a sampling data identification method thereof, and a program for identifying sampling data.
2. Description of the Related Art
A seismometer for monitoring ground tremors at a certain monitoring point and an apparatus for recording earthquake motion waveforms thereof are already known. In this case, the recording apparatus receives an analog signal, which corresponds to the ground motion at the aforementioned monitoring point, from the seismometer provided at that point. In addition, the recording apparatus also generates timing data that is synchronized with sampling time obtained by dividing a reference clock signal produced by an oscillator (for example, a quartz crystal oscillator). The recording apparatus then subjects the analog signal from the sensor to A/D conversion at a timing that is synchronized with the sampling time in order to produce digital data. The recording apparatus then records this digital data together with the aforementioned sampling time. Since this recorded digital data and sampling time are, for example, used to identify the location of the hypocenter of an earthquake or to estimate the subsurface structure of locations to which seismic waves were transmitted or the like, it is necessary to know the exact sampling time at which each piece of digital data was sampled.
However, since the oscillation frequency of a reference clock signal, which defines the timing that is synchronized with the sampling time, may deviate from an oscillation frequency for generating an exact time, there is a problem that in some cases the exact sampling time can not be recorded.
Technology that attempts to solve this problem is disclosed in Japanese Laid-Open Patent No. 2004-29037 and Japanese Laid-Open Patent No. 2002-122447.